1. Field of the Invention
The present invention relates to a head of a wrench handle with an improved torque-bearing capacity without increasing the manufacturing cost of the wrench.
2. Description of the Related Art
FIG. 1 of the drawings illustrates a handle head 100 of a conventional spanner type ratchet wrench. A gear 104 is rotatably mounted in a hole 100a in the head 100 and includes a polygonal inner periphery 101 for driving a fastener. The head 100 further includes a compartment 102 communicated with the hole 100a of the head 100. A pawl 103 is mounted in the compartment 102 and engaged with the gear 104. During ratcheting operation, the pawl 103 bears against a wall defining the compartment 102 at 105, which corresponds the third teeth counting from the leftmost tooth of the pawl 103 in FIG. 1. As can be seen from FIG. 1, the right portion of the pawl 103 is not supported such that when the force imparted to the pawl 103 reaches a critical value, no reactive force is obtained, and the pawl 103 will be disengaged from the gear 104 and move like a seesaw. The first three teeth will be damaged. This is owing to the fact that the compartment 103 is too shallow such that the pawl 103 merely engages with the gear 104 by only three effective teeth during the ratcheting operation. As a result, the torque-bearing capacity of the pawl 103 is poor. Enlargement of the head 100 would improve the torque-bearing capacity, yet the enlargement would contradict the benefit of the use of the spanner type ratchet type in a limited space.
FIG. 2 illustrates a pawl 106 having two centers E and F of curvatures. Namely, the pawl 106 includes a toothed side having a first teeth section 106a with a center E of curvature and a second teeth section 106b with a center F of curvature located at a position other than the center E of curvature. This allows more teeth of the pawl 106 in the compartment 108 to engage with the teeth 107a of the drive gear 107 of the wrench. Thus, during ratcheting, the second teeth portion 106b would not engage with the drive gear 107 when the first teeth portion 106a engages with the drive gear 107 and vice versa. This allows a stable, balanced operation of the pawl 106 during ratcheting, and the torque-bearing capacity was improved by 30%. Such a pawl has been disclosed in Applicant""s U.S. patent application Ser. No. 09/523,625 filed on Mar. 13, 2000.
FIG. 3 illustrates a handle head of another wrench. The head 109 comprises a hole 109c for rotatably receiving a drive gear 109d. The head 109 further includes a compartment 109a communicated with the hole 109c, and a pawl 110 is slidably received in the compartment 109a. A cavity 109e is defined in a wall defining the compartment 109a, and a rigid pin 109b is fixed in the cavity 109e. The pawl 110 includes a toothed first side and a second recessed side 110c having two inclined faces 110e. The pawl 110 further includes two ends 110b. Thus, during ratcheting, the pawl 110 is supported at one of the ends 110b that bears against a side of the wall defining the compartment 109a and at one of the inclined faces 110b that bears against the rigid pin 109b. Almost all of the teeth of the pawl 110 are engaged with the drive gear 109d. Undesired disengagement of the pawl 110 from the drive gear 109d is prevented, and the torque-bearing capacity is improved. But the manufacturing cost is increased. Such a wrench has been disclosed in Applicant""s U.S. patent application Ser. No. 09/916,796 filed on Jul. 27, 2001.
An object of the present invention is to provide a head of a wrench handle with an improved torque-bearing capacity without increasing the manufacturing cost of the wrench.
In accordance with one aspect of the invention, a head of a wrench comprises a hole having a center and a radius. The head further includes a compartment communicated with the hole. A wall defining the compartment has a center of curvature and a radius of curvature. A ratio between the radius (RB) of curvature of the wall and the radius (RA) of the hole and is defined as follows:
(0.5xe2x89xa6RB/RA less than 1)
and
A distance (R1) between the center of the hole and the center of curvature of the wall is defined as follows:
R1 greater than RAxe2x88x920.328*RB
The present invention also provides a way to figure out a pawl for cooperating with the compartment thus formed.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.